So there is nothing wrong with his visiting his sister’s
daughter and being alone with her or travelling with her, so long as there
are no reasons for suspicion, such as if he is an evildoer and cannot be
trusted with his sister’s daughter. If there are any grounds for suspicion,
then he is not allowed to be alone with or visit her when her husband is not
present.

Some of the salaf – such as ‘Ikrimah and al-Sha’bi – were of
the view that even though it is not permissible for a paternal uncle or a
maternal uncle to marry their sister’s daughter or brother’s daughter, it is
nevertheless not permissible for her to show her adornment in front of them,
and she must observe hijab with them. They quoted two things as evidence for
that:

1 – The maternal uncle and paternal uncle are not mentioned
in the verse of Soorat al-Ahzaab which says that it is permissible for a
woman to show her adornment in front of her mahrams. Allaah says
(interpretation of the meaning):

“It is no sin on them (the Prophet’s wives, if they appear
unveiled) before their fathers, or their sons, or their brothers, or their
brother’s sons, or the sons of their sisters, or their own (believing)
women, or their (female) slaves. And (O ladies), fear (keep your duty to)
Allaah. Verily, Allaah is Ever All‑Witness over everything”

[al-Ahzaab 33:55]

Here Allaah does not mention the paternal uncle or maternal
uncle.

2 – They said: and because a maternal uncle or paternal uncle
may describe the woman to his sons.

But the majority of scholars are of the view that the
maternal uncle and paternal uncle are among the mahrams in front of whom it
is permissible for a woman to show her adornment. In response to the comment
that the maternal uncle and paternal uncle are not mentioned in the verse,
they said:

They are not mentioned because their status is like that of
the parents, hence Allaah calls the paternal uncle a father, in the verse in
which He says (interpretation of the meaning):

“Or were you witnesses when death approached Ya’qoob (Jacob)?
When he said unto his sons, ‘What will you worship after me?’ They said, ‘We
shall worship your Ilaah (God — Allaah) the Ilaah (God) of your fathers,
Ibraaheem (Abraham), Ismaa’eel (Ishmael), Ishaaq (Isaac), One Ilaah (God),
and to Him we submit (in Islam)’”

[al-Baqarah 2:13]

Ismaa’eel was the paternal uncle of Ya’qoob (peace be upon
them both)

2 – They are not mentioned because it is sufficient to
mention the brother’s son and sister’s son, so it is more appropriate that
this ruling should apply to the paternal uncle and maternal uncle.

Al-Sa’di (may Allaah have mercy on him) said (p. 788):

“It is no sin on them” means if they do not observe
hijab in front of them. No mention is made here of paternal uncles and
maternal uncles because if women do not have to observe hijab in front of
those whose paternal and maternal aunts they are, the sons of their brothers
and sisters, even though they (these women) are of a higher status than
them, then it is more likely that they do not have to observe hijab in front
of their paternal and maternal uncles. End quote.

With regard to the reason given, that the maternal uncle or
paternal uncle may describe the woman to their sons, the majority of
scholars responded to this by noting that this is a weak argument, because
if this is accepted, it would imply that it is not permissible for a woman
to uncover her adornment in front of any woman, because she may describe her
to her sons!

One thing which indicates that the view of the majority –
that it is permissible for a woman to show her adornment to her paternal and
maternal uncles, and that it is permissible for them to enter upon her and
be alone with her – is correct is the report narrated by al-Bukhaari (4796)
and Muslim (1445) from ‘Aa’ishah (may Allaah be pleased with her), who said:
Aflah, the brother of Abu’l-Qu’aysh, asked for permission to enter upon me
after the (verse of) hijab had been revealed, and I said, I will not let him
in until I ask the Prophet (peace and blessings of Allaah be upon him)
for permission, because his brother Abu’l-Qu’ays is not the one who
breastfed me, rather the wife of Abu’l-Qu’ays breastfed me. The Prophet
(peace and blessings of Allaah be upon him) entered upon me and I said to
him: “O Messenger of Allaah, Aflah, the brother of Abu’l-Qu’aysh, asked for
permission to enter upon me, but I refused to let him in until I asked your
permission. The Prophet (peace and blessings of Allaah be upon him)
said: “What kept you from letting him in? He is your paternal uncle!” I
said, “O Messenger of Allaah, the man is not the one who breastfed me,
rather the wife of Abu’l-Qu’ays breastfed me.” He said: “Let him in, for he
is your paternal uncle, may your right hand be rubbed with dust.” So if a
paternal uncle through breastfeeding is allowed to enter upon a woman and be
alone with her, then it is more appropriate that a paternal uncle through
blood ties be allowed to do so, and the same applies to the maternal uncle.